Coalescence and separation in binary collisions of liquid drops

Ashgriz, Nasser; Poo, J. Y.

doi:10.1017/s0022112090003536

Cited by 620 publications

(609 citation statements)

References 22 publications

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“…Previous studies [25][26][27] have demonstrated that droplet separation is suppressed and hence droplet coalescence is promoted by increasing the size ratio. It is known that droplet separation occurs, at relatively high Weber numbers, when the surface tension of the temporarily coalesced droplet cannot hold the excess kinetic energy of the collision.…”

Section: Collision Dynamics and Internal Mixing Of Dropletsmentioning

confidence: 98%

Hypergolic ignition by head-on collision of N,N,N′,N′ −tetramethylethylenediamine and white fuming nitric acid droplets

Zhang

Yuan

et al. 2016

Combustion and Flame

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a b s t r a c tHypergolic ignition by the head-on collision of a smaller N,N,N ,N −tetramethylethylenediamine (TMEDA) droplet and a larger white fuming nitric acid (WFNA) droplet was experimentally investigated by using a droplet collision experimental apparatus equipped with a time-resolved shadowgraph, a photodetector and an infrared detector. The investigation was focused on understanding the influence of droplet collision and mixing, which vary with the collisional Weber number ( We = 20 −220) and the droplet size ratio ( = 1.2 −2.9) while have a fixed Ohnesorge number (Oh = 2.5 ×10 −3 ), on the hypergolic ignitability and the ignition delay times. The hypergolic ignition was found to critically rely on the heat release from of the liquid-phase reaction of TMEDA and nitric acid, which is subsequent to and enhanced by the effective mixing of the droplets of proper size ratios. Consequently, the ignitability regime nomogram in the We-space shows that the hypergolic ignition favors small s and large We s; the ignition delay times tend to decrease with either decreasing , or increasing We , or both. A non-monotonic variation of the ignition delay times with We was observed and attributed to the non-monotonic emergence of jet-like mixing patterns that enhance the droplet mixing and hence the liquid-phase reaction.

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Section: Collision Dynamics and Internal Mixing Of Dropletsmentioning

confidence: 98%

Hypergolic ignition by head-on collision of N,N,N′,N′ −tetramethylethylenediamine and white fuming nitric acid droplets

Zhang

Yuan

et al. 2016

Combustion and Flame

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“…This occurs for sufficiently low viscosities and for coalescence from an initially motionless state and is a phenomenon well known from studies of droplets falling into a liquid pool [18][19][20][21][22]. An extensive experimental study of binary midair drop collisions in air was conducted by Ashgriz and Poo [17], who characterized different regimes of coalescence and separation in terms of Weber number and an impact parameter measuring the degree to which the drop centers were offset from a head-on collision. Since one of the drops was dyed, this study also revealed that for offset collisions, substantial mixing can occur within the combined drop as a result of the free-surface deformations.…”

Section: Introductionmentioning

confidence: 99%

“…An effective visualization of mixing in this case has been a simple coloring of one of the droplets [16,17]. A key observation when a small droplet coalesces with a larger one is the generation of a vortex ring [16] as the small droplet is pulled into the larger one by surface tension.…”

Section: Introductionmentioning

confidence: 99%

“…We aimed to separate the effects of other variables such as drying, curing, and density and viscosity gradients from purely dynamical effects. To provide a clear picture of the mixing, the approach of coloring one of the droplets, which has been useful in visualizing the mixing during in-air coalescence of two free droplets [17] and two sessile droplets [23], is applied. The experimental results are compared with numerical simulations by the lattice Boltzmann method showing that mixing is not achieved within the combined volume of the coalescing droplets.…”

Section: Introductionmentioning

confidence: 99%

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Mixing and internal dynamics of droplets impacting and coalescing on a solid surface

et al. 2013

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The coalescence and mixing of a sessile and an impacting liquid droplet on a solid surface are studied experimentally and numerically in terms of lateral separation and droplet speed. Two droplet generators are used to produce differently colored droplets. Two high-speed imaging systems are used to investigate the impact and coalescence of the droplets in color from a side view with a simultaneous gray-scale view from below. Millimeter-sized droplets were used with dynamical conditions, based on the Reynolds and Weber numbers, relevant to microfluidics and commercial inkjet printing. Experimental measurements of advancing and receding static contact angles are used to calibrate a contact angle hysteresis model within a lattice Boltzmann framework, which is shown to capture the observed dynamics qualitatively and the final droplet configuration quantitatively. Our results show that no detectable mixing occurs during impact and coalescence of similar-sized droplets, but when the sessile droplet is sufficiently larger than the impacting droplet vortex ring generation can be observed. Finally we show how a gradient of wettability on the substrate can potentially enhance mixing.

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“…At larger velocities, the liquid distorts so dramatically that there is fragmentation of the filaments forming during impact (Ashgriz & Poo 1990;Jiang, Umemura & Law 1992). The phase diagram of impacts is of central importance in different fields where coalescence is either looked for, or unwanted.…”

Section: Introductionmentioning

confidence: 99%

Water colliding with oil

Quéré

2012

J. Fluid Mech.

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The collision of two liquid drops is both an applied question (in rain formation or combustion, for example) and a beautiful basic situation, where impact involves liquid phases, making this problem worth studying in its own right. In a stimulating paper, Planchette, Lorenceau & Brenn (J. Fluid Mech., this issue, vol. 702, 2012, pp. 5-25) consider collisions between oil and water, which often lead to water drops protected by a shell of oil. By looking at the deformations during impact, they characterize the dynamical conditions leading to single encapsulation, and derive a criterion for avoiding fragmentation.

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Coalescence and separation in binary collisions of liquid drops

Cited by 620 publications

References 22 publications

Hypergolic ignition by head-on collision of N,N,N′,N′ −tetramethylethylenediamine and white fuming nitric acid droplets

Hypergolic ignition by head-on collision of N,N,N′,N′ −tetramethylethylenediamine and white fuming nitric acid droplets

Mixing and internal dynamics of droplets impacting and coalescing on a solid surface

Water colliding with oil

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